The software he (ebay) is talking about is most likely
PS2 Linux kernelloader 2.7, with
Free McBoot on the memory card in order to boot the .ELF
The software is as says, totally free. But $20 for an 8mb memory card is a little steep.
If you would like, I could install this software on a memory card and send it to you. Either send me one of your memory cards or I could pickup a second hand one, install the software, and mail it. I would only charge you the cost of the card and postage. This will allow you to do anything basically. Install official sony linux on a non-sony HDD, install non-official linux, run homebrew, ect.
The Playstation 2 was the system that got me into the "hacking scene" per se. My original intent as a teen was to play SNES emulators on the PS2, so I found the cheapest way to bypass Sony's copy protection (disc swap method) in order to play homebrew. I know the system inside and out, it has a special place in my heart :wub:
Free McBoot basically uses an exploit in the PS2 OS. When the system turns on, it checks the memory card for any updates (there was really only one PS2 menu update, in Japan). People eventually found a way to trick the system into accepting a hacked .ELF as an update that exploited the OS, allowing it to run anything the user desires. Your system does not have to be opened or physically modified in any way for this to work. Just plug the memory card with Free McBoot installed into the PS2 and go. To unmod, remove the memory card and reset, it's that simple.
The only downfall to this exploit, is you need a way to install Free McBoot on a memory card, and the only way to do that is with a PS2 already modded. (This is where I come in

)
I no longer use any type of hardware exploit. Free McBoot does everything I would ever need. Any other exploit/hack might have some speed or compatibility advantages, but FMCB (for the most part) has a workaround.
The only info about your system that I will need is the model version.
PS2 version identification. You can also list off any 3rd party PS2 software you may have (ARMax, Codebreaker, Swap Magic, ect). You may be able to install FMCB yourself!